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Can you charge a battery with another battery?

  1. Jun 30, 2015 #1
    To do this would you simply run the current from one battery through another in reverse? Would there be a significant loss in energy?
     
  2. jcsd
  3. Jun 30, 2015 #2

    mfb

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    It is not impossible in general, but it can lead to bad consequences (including exploding batteries) if done improperly. Just don't do it.
     
  4. Jun 30, 2015 #3

    berkeman

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    As mfb says, not directly. But there are battery-based battery chargers that have circuitry inside that makes the charging process safe and relatively efficient:

    http://www.schoolmart.com/images/products/detail/EVOPowerPlusintocell.jpg [Broken]
    http://www.schoolmart.com/images/products/detail/EVOPowerPlusintocell.jpg [Broken]
     
    Last edited by a moderator: May 7, 2017
  5. Jun 30, 2015 #4
    Ok, what about a capacitor charging a capacitor? And would charge be lost?
     
    Last edited by a moderator: May 7, 2017
  6. Jun 30, 2015 #5

    berkeman

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    Charge is conserved, but some energy is lost in the transfer of charge from one capacitor to another. In fact, it is a common FAQ to figure out where the energy goes... :smile:
     
  7. Jun 30, 2015 #6
    Ok lastly, what happens if you add two different quantities of charge with different voltages to a single capacitor? How would they come out in the discharge of the capacitor?
     
  8. Jun 30, 2015 #7

    mfb

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    That question does not make sense. You cannot "add a charge of X at voltage Y", the voltage is determined by the amount of charge and the capacitance (and it changes during the charging process).
     
  9. Jun 30, 2015 #8
    sorry, If i charge a capacitor with a 12 volt battery for 30 seconds, then I charge it with a 9 volt battery for 30 seconds, what voltage will come back out of the capacitor? Hope that makes more sense.
     
  10. Jun 30, 2015 #9
    It might be more relevant to ask how much smoke will come out of the battery.
     
  11. Jun 30, 2015 #10

    Drakkith

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    That depends on several factors, including the capacitance of the capacitor. If the capacitance is too small, then the capacitor is completely charged to 12 volts and connecting a 9-volt battery to it will probably damage the battery. If its very large then the 12v battery will not charge it to even 9 volts and you can then connect the 9v battery and charge it to 9v.

    See here for more info: http://www.electronics-tutorials.ws/rc/rc_1.html
     
  12. Jul 5, 2015 #11
    Do we know where the energy goes?
     
  13. Jul 6, 2015 #12

    berkeman

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    Yes we do. :smile:
     
  14. Jul 6, 2015 #13
    You need higher potential to charge a battery. So if you are charging a 12V battery you would need 13-14V of any current throughput to charge that 12V bat.
     
  15. Jul 7, 2015 #14
    There's some resistance and inductance in the circuit which can't be ignored when dealing with capacitors. If the inductance is negligible, then the RC product determines the charging or discharging time. With inductance, you can get damped oscillations.
     
  16. Jul 9, 2015 #15
    Is there a way to calculate the energy lost through oscillations? If so can you show me or direct me to a link? Thanks for the help sir
     
  17. Jul 10, 2015 #16

    CWatters

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    Some years ago it was discovered that certain sub C size NiCad cells performed better in RC cars and competition aircraft after they had been "zapped". The zapping process involved charging up a bank of capacitors the size of a shoebox and discharging them into the cell using an SCR the size of a hockey puck (I heard early experiments involved using a garden spade as a switch!). The wires connecting the capacitors to the cells would twitch due to the high current and earths magnetic field. A very high percentage of the cells survived.

    Do not try this at home! It's very dangerous.
     
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